U.S. Pat. No. 3,617,233 (Mumford), which was assigned to a predecessor of the assignee of this application, the disclosure of which is incorporated by reference herein, describes a glass forming machine of the I.S. type, which is a type of forming machine that is widely used in forming various types of hollow glass containers. As described in the '233 patent or as is otherwise known, an I.S. machine has a multitude of side-by-side machine sections, such as six, eight, ten or even twelve sections, and containers are formed in each section, usually two, three or four at a time, in a two-step process. In the first of the steps, preforms of the containers, which are often called parisons or blanks, are formed by pressing or blowing gobs of molten glass in a first set of molds, often called blank molds, with each container parison being formed in an inverted orientation, that is, with its open end down. Each set of blank molds is made up of a separable pair of semi-cylindrical mold elements, which remain in end to end contact with one another throughout the blank molding step.
During the forming of glass parisons in an I.S. machine blank mold, the "finish" portion of the parison, which is the threaded or otherwise configured closure receiving portion at the open end, is formed by a separate annular neck mold, which is often referred to as a neck ring, each of which is made up of a separable pair of generally semi-cylindrical elements. The neck rings for each I.S. machine section are carried in a neck ring mechanism and remain in closing contact with the parisons at the conclusion of the blank molding step, when the elements of the blank molds separate to allow the parisons to be transferred to a second set of molds, often referred to as blow molds, for the blowing of parisons into containers in the final desired shape of the containers. The containers are held by the neck rings during their transfer from the blank molds to the blow molds, and the transfer is effected by inverting the neck ring mechanism through an arc of 180.degree. to present the parisons, which remain grasped by the neck rings throughout the transfer step, at the blow molds, the parisons now being in upright orientations, with the finishes at the top, as a result of the inverting step.
When the parisons arrive at the blow molds, they are released by the neck rings to permit the neck ring mechanism to revert to its location at the blank mold station, by a movement in a reverse arc of 180.degree., to begin a repeat of the two-step manufacturing process. The neck ring mechanism is made up of a separable side by side pair of arm segments, and the segments separate at the blow mold station, which causes the elements of the neck ring assembly that are carried by the neck ring mechanism to separate, to thereby release the parisons into the blow molds. The alternate separation and rejoining of the neck ring mechanism arm elements is accomplished by a reciprocating motion of each element with respect to a horizontal shaft which passes through an end portion of such arm element, and the oscillation of the neck ring mechanism is caused by oscillating the shaft, which is often referred to as an invert shaft or a rock shaft, through an arc of 180.degree., each arm element being rotatable with, but not with respect to, the invert shaft. Another version of a neck ring mechanism for an I.S. glass forming machine is disclosed in U.S. Pat. No. 3,233,999 (Mumford), which was also assigned to a predecessor of the assignee of this application, the disclosure of which is also incorporated by reference herein.
Prior art neck ring mechanisms typically used spline connections between the arm elements and the invert shaft to permit sliding motion of the arm elements relative to the shaft while ensuring that the arm elements oscillate with the shaft. Such spline connections are subject to backlash, however, thus making precise positioning of the neck ring assembly arm elements with respect to one another difficult to achieve, and this factor, which can lead to improperly formed container finishes, worsens with usage due to wear. This requires frequent replacement of the neck ring mechanism, replacement of one or more of its elements being impractical, which involves a shutdown of the machine section for a prolonged duration with a loss of its productive capacity.
Another problem encountered with prior art neck ring mechanisms that involved a splined connection between the invert shaft and the neck ring arm elements is that the reciprocation of the arm elements relative to the invert shaft typically is primarily spring actuated, pneumatic actuation not being reliable due to air leakage in use because of the inability to properly seal a splined shaft against such leakage.